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PCBD-Oct2017

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October 2017 • The PCB Design Magazine 49
The problem with DDR5 topologies tends to be
ringing—not loss. Serial channels are point to
point, and discontinuities are stubs are sharply
minimized to maximize signal quality. DDR5
topologies, by comparison, cannot afford to
manage impedance and discontinuities as tight-
ly—it's just not economically feasible. Because
DDR5 topologies are multi-drop, multi-DIMM,
stubs are long and reflections are huge by com-
parison. That's why we're so interested to see
how the use of DFE plays out in DDR5, because
DFE technologies are uniquely suited for deal-
ing with significant reflections in the few bit
times that precede the main signal.
Shaughnessy: How would users use AMI models
to determine the best equalization settings for
their systems?
Katz: There are two users, and they want to
know two different things: The systems designer
wants to know that for a given channel there is
a best set of equalization settings that will opti-
mize the DDR5 channel performance (smallest
BER, largest time and voltage margins), and that
the BER and timing and voltage margins meet
the system performance requirements. They
also want to know that whatever training algo-
rithm the controller uses to optimize the chan-
nel at hardware runtime will end up with the
settings needed to properly equalize the chan-
nel. So the systems designer wants to be able to
predict the effect of the hardware training al-
gorithm on system margin without necessarily
modeling that training algorithm literally.
But the device vendor wants to design and
validate the hardware training algorithm and
prove that it will reach or at least come close to
the best performance of the channel. They do
want to model the training algorithm literally,
or very nearly so.
Shaughnessy: It sounds like this whole thing
has a lot of layers. Maybe we should talk again
after DDR5 launches, to see how people are do-
ing with this?
Katz: This is an incredibly detailed and inter-
esting problem. What the actual hardware does
and what the simulation models do will not be
the same. Effectively managing the details of
those differences will be critical to maximize
the design's chance for success.
Shaughnessy: Thanks for your time, Walter.
Katz: Thank you, Andy.
PCBDESIGN
SISOFT PREPARING FOR DDR5 SIMULATION NEXT YEAR
Researchers have created a min-
iature 'superhero' robot capable of
transforming itself with different
'outfits' to
perform a variety of tasks.
Inspired by origami, scientists
from the University of York and the
Massachusetts Institute of Technolo-
gy (MIT) have developed a magnet-
controlled shape-shifting device which can walk, roll,
sail on water or glide.
Dubbed "Primer," the cube-shaped robot carries
out these actions by wearing different exoskeletons—
accessories which start out as sheets of plastic that
fold into specific shapes when heated. After Primer
finishes its task, it can shed its "skin" by immersing
itself in water, which dissolves the exoskeleton.
Professor Daniela Rus, Director
of MIT CSAIL and Principal Investi
-
gator on the project, said:
"If we
want robots to help us do things,
it's not very efficient to have a dif-
ferent one for each task. With this
metamorphosis-inspired approach,
we can extend the capabilities of a
single robot by giving it different accessories to use
in different situations."
While robots that can change their form or func-
tion have been developed at larger sizes, generally
it's
been difficult to build such structures at much
smaller
scales. What is also new about Primer is its
ability to switch between many, rather than several,
different forms.
Scientists Develop Shape-Shifting 'Superhero' Robot